Publication Date: April 2009
Publication No. 17: Ozone Treatment of
Private Drinking Water Systems
Effective Against: Pathogenic (disease-causing) organisms including bacteria and viruses, phenols
(aromatic organic compounds), some color, taste and odor problems, iron, manganese, and turbidity.
Not Effective Against: Large cysts and some other large organisms resulting from possible or probable
sewage contamination, inorganic chemicals, and heavy metals.
How Ozone (O3) Treatment Works
Ozone is a chemical form of pure oxygen. Like chlorine, ozone is a strong oxidizing agent
and is used in much the same way to kill disease-causing bacteria and viruses. It is effective
against most amoebic cysts, and destroys bacteria and some aromatic organic compounds
(such as phenols). Ozone may not kill large cysts and some other large organisms, so these
should be eliminated by filtration or other procedures prior to ozone treatment. Ozone is
effective in eliminating or controlling color, taste, and odor problems. It also oxidizes iron
and manganese.
Ozone treatment units are installed as point-of-use treatment systems. Raw water enters one opening and
treated water emerges from another. Inside the treatment unit, ozone is produced by an electrical corona
discharge or ultraviolet irradiation of dry air or oxygen. The ozone is mixed with the water whenever the
water pump is running. Ozone generation units require a system to clean and remove the humidity from the
air. For proper disinfection the water to be treated must have negligible color and turbidity levels. The
system requires routine maintenance and an ozone treatment system can be very energy consumptive.
Ozone is not without some concerns also; ozone is a toxic gas and it can produce disinfection by-products
in drinking water. In order to reduce by-product formation, the water must have minimal amounts of
The major benefit of ozone treatment is that it is very effective as a disinfectant. In contrast to chlorine,
ozone is active over a wide pH and temperature range. The required contact time is so short that it is not a
consideration in the system design. However, this is not true for Giardia and Cryptosporidium, both
protozoan cysts associated with sewage contamination.
Always follow the manufacturer’s instruction for maintenance, cleaning, and part replacement. Regardless
of the quality of the equipment purchased, it will not perform satisfactorily unless maintained in accordance
Produced by The State of Connecticut Department of Public Health
Environmental Health Section, Private Well Program
450 Capitol Avenue, MS#51REC, PO Box 340308, Hartford, CT 06134
Phone: 860-509-7296 Fax: 860-509-7295
Page 1 of Publication No. 17: Ozone Treatment of Private Drinking Water Systems
with the manufacturer’s recommendations for maintenance, cleaning, and part replacement. Keep a
logbook to record equipment maintenance and repairs.
Other Considerations
Ensure the system you choose is installed and operated according to the manufacturer’s
instructions after installation. Retest both the raw water (prior to treatment) and the
treated water at a state certified laboratory to ensure the system is working properly and
removing the contaminants. You should continue to test the quality of both the raw and
treated water annually or more frequently (quarterly or semi-annually) if high levels of
contaminant are present in the raw water. Frequent testing will also help you determine how well your
treatment system is working and whether maintenance or replacement of components may be necessary.
Like chlorine, ozone is a toxic gas and ozone generators may lead to and could create an ozone hazard
within your home, causing illness. The greatest drawback with ozone treatment is its lack of an ozone
residual time. With ozone treatment, disinfection occurs primarily at the point of contact between the ozone
and the water. The disinfection process does not occur beyond the treatment unit. This contrasts with
chlorination treatment where the residual chlorine remains in the water and continues the disinfection
process for some time. Ozone has an active residual time measured in minutes, whereas the active residual
time for chlorine is measured in hours. You can purchase equipment to test for residual ozone. The only
way to know if the unit is working is to test for ozone residual or have bacterial tests conducted on the
treated water. Ozonation equipment is expensive, and chlorination may still be desirable because of the low
residual time of ozone.
Questions to Ask Before You Buy
Before purchasing a water treatment device, have your water tested at a state certified laboratory to
determine the contaminants present. This will help you determine if microfiltration is a viable alternative
treatment method for your situation. See the #19 Questions to Ask When Purchasing Water Treatment
Equipment for more information. Consumers should inquire about the following before purchasing an
ozone system:
Has the treatment system been tested and certified by a third party to ensure that it meets manufacturer’s
Are there any special installation requirements that may add to the equipment costs, for instance
changes to your household plumbing?
Product Certification
NSF International is a non-profit organization that sets performance standards for water treatment
devices. Because companies can make unsubstantiated statements regarding product
effectiveness, the consumer must evaluate test results of the device to determine if claims are
realistic. Products that have been tested or evaluate by NSF and meet their minimum
requirements are entitled to display the NSF listing mark on the products or in advertising literature for
products. Manufacturers and models that meet NSF’s standard are included in a listing published twice a
year. For more information contact NSF at 1-800-NSF-MARK or http://www.nsf.org/consumer/
For more information please click on the following links:
EPA Office of Groundwater and Drinking Water
EPA New England
Adapted from Healthy Drinking Waters for Rhode Islanders, University of Rhode Island Cooperative Extension, April 2003.
Page 2 of Publication No. 17: Ozone Treatment of Private Drinking Water Systems